Lenticular images include an array of cylindrical lenses in a lenticular material and a sequence of spatially multiplexed images that are viewed through the lenticular material so that different ones of the multiplexed images are viewed at different angles by the viewer. One image effect produced by the lenticular image is a stereoscopic image, sometimes referred to as a depth image, where the lenticules are oriented vertically. One eye of a viewer sees one image of a stereo pair of images from one angle and the other eye of the viewer sees another image from the stereo pair of images. Another available image effect is a so called motion image, where different images in a sequence of images are viewed by both eyes, while the angle at which the image is viewed changes. In this image effect the lenticules are oriented in the horizontal direction and the lenticular material is rotated about the long axis of the lenticules. Other effects that combine these two effects, or form collages of unrelated images that can be viewed from different viewing angles can be provided.
It has been proposed to create stereoscopic images by providing a lenticular material having a color photographic emulsion thereon. The stereoscopic images are exposed onto the lenticular material by a laser scanner and the material is processed to produce the lenticular image product. See for example, U.S. Pat. No. 5,697,006, which issued Dec. 9, 1997 to Taguchi et al.
The image that is exposed on the lenticular material must be very precisely positioned under each lenticule. If the separate image lines produced by the writing laser beam of the laser scanner and the lenticules on the material are not aligned parallel, the resulting skew misalignment will degrade the image quality. There is a need therefore for an improved manufacturing process for making lenticular image products from lenticular material of the type having a lenticular lens array coated with photographic emulsion.
It is known to scan a non-actinic laser beam across a lenticular array in a direction perpendicular to the axes of the lenticules, and to sense the deflection of the beam by the lenticules to produce an output clock for modulating a writing laser beam. See U.S. Pat. No. 5,681,676, issued to Telfer et al. on Oct. 28, 1997.
Commonly assigned, co-pending U.S. patent application Ser. No. 09/217,030 entitled DETECTION AND CORRECTION OF SKEW BETWEEN A REFERENCE AND LENTICULES IN LENTICULAR MATERIAL, filed Dec. 21, 1998 in the names of Cobb et al. discloses a skew detection and correction process for forming a lenticular image product from a lenticular material having an array of cylindrical lenses. The lenticular material is scanned with a writing laser beam of light along a direction parallel to the long axes of the cylindrical lenses to form a latent lenticular image in photographic emulsion. A alignment beam of light having a wavelength outside of the range of sensitivity of the photographic emulsion is focused into a spot smaller than the pitch of the cylindrical lenses and onto the lenticular material. The lenticular material is moved through the beams to provide a page scan motion across the short axes of the lenticules of the material and to modulate the angle of reflection or refraction of the alignment beam of light caused by the lenticules. The position of the angularly-modulated alignment beam of light is sensed at two separated points along the long axes of a lenticule, and the sensed positions are used to control the rotational position of a pivoting cylinder mirror assembly. As a result, the skew between the writing laser beam and the long axes of the cylindrical lens is minimized and the parallel alignment of the writing laser beam to the lenticule is maintained.
Although the skew detection and correction process disclosed in the Cobb et al. application is believed to work well for its intended function, it cannot, however, determine if the skew error of the writing laser beam, relative to the media, is greater than a whole lenticule. For example, given a detector separation "w" of, say, 5 inches and a lenticule pitch "p" of, say, 0.015 inches, then the skew error "p/w" radians would be 0.17.degree.. The Cobb et al. system would be unable to distinguish between this hypothetical condition and a perfectly aligned condition. In use, a skew alignment of this magnitude would result in a completely unacceptable print. Similarly, if the skew error were greater than half of this error (for example, a skew error of 1/2*p/w+.epsilon., where .epsilon. is a small value), then the sensing system disclosed in the Cobb et al. application would predict an error of -(1/2*p/w-.epsilon.). This result would be wrong by an amount "p/w", or a single lenticule of skew error. Accordingly, while the system disclosed in the Cobb et al. application would provide a correct result in most situations, it will only be correct if the skew error is less than 1/2*p/w. For errors greater than this angle, the detector system cannot determine the correct skew angle error.